Method of decreasing the wear of flexible bodies rubbing on a rigid surface

ABSTRACT

A method of decreasing wear on flexible bodies caused by rubbing on rigid surfaces is shown. The rigid surface is coated with a paraffin composition, preferably paraffin or petroleum wax. Improved stability of the composition, with time, is obtained by incorporating, in the composition, an additive such as polyethylene. The compositions are applied to rigid surfaces such as concrete by spraying or by roller application. In the former case the compressed air for the spray gun and the surface to be coated are heated. The coatings may be advantageously applied to concrete tracks upon which air cushion (hover) vehicles are guided.

United States Patent [1 1 Kennel et a1.

[ Get. 23, 1973 2,397,305 4/195 Qtt..... 106/2 30 METHOD OF DECREASING THE WEAR 0F FLEXIBLE BODIES RUBBING ON A RIGID SURFACE Inventors: Michael Kennel; Yves Drapeau, both of Le Havre, France Assignee:

Compagnie Francaise De Raffinage,

Paris, France Filed: v

July 26, 1972 Appl. No.: 275,359

Related US. Application Data Continuation-impart of Ser. No. 62,169, Aug. 7, 1970, abandoned.

Foreign Application Priority Data Aug. 8, 1969 July 8,1970 Belgium ..70753146 July 15, 1970 Italy ..70900585 115 9.2-..Ii hr e 1s .LZQZQLQQLQ US. Cl. 117/123 E, 117/652, 117/168,

252/5'9, 117/123 D, 260/285 AV Int. Cl C04b 41/00 Field of Search 106/270, 273, 285;

France 6920 55945 117/123 D, 123 E, 132 C, 135,148, 149,

References Cited UNITED STATES PATENTS 2,499,723 3/1950 Coffman et al. 252/56 3,025,560 3/1962 Lindner 252/12 X 3,175,972 3/1965 Mitacek et al..... 252/59 X 3,258,319 6/1966 Cox 252/59 X 3,438,896 4/1969 Council et a1. 252/12 X 3,462,249 8/1969 Tunkel 252/59 X 3,607,746 9/1971 Caruso 252/12. 3,647,693 3/1972 Crookshank 1. 252/59 X Primary ExaminerWilliam D. Martin Assistant Examiner-M. R. Lusignan Attorney-A. Thomas S. Safford et al.

[57] ABSTRACT 'The'coatings may be advantageously applied to concrete tracks upon which air cushion (hover) vehicles are guided.

2 Claims, 6 Drawing Figures United States Patent 1 [111 3,767,460

Kennel et al. Oct. 23, 1973 SPE'ED Ira/fr METHOD OF DECREASING THE WEAR OF FLEXIBLE BODIES RUBBING ON A RIGID SURFACE the wear of flexible bodies which rub, at high speed, on those rigid bodies. Even more specifically, it'relatesxto rigid bodies covered with awear reducing composition; It is known that flexible bodies such as naturaland synthetic rubber, plastics, leather and synthetic compounds capable of replacing leather, can become'worn.

very rapidly by rubbing against arigidmaterial; partic-' ularly when the speedofrubbing ishigh: Thisis'particularly true where the flexible-body rubs: on bare concrete or even on concrete which has beencoveredwith:

some protective coatings.

By highspeed-is meantzspeeds higher than those encountered in movements lubricatedby mixtures containing paraffins and greases, such as, for;example,*the. launching. of ships which takes: place at very low speeds" of the order of to km/hr'at-themost; More specif-" ically, high speed means speedsat'which-the-lubrication of the movement of asoft-bodyrubbing againsta rigid surface can-nolonger be effectedby priorart compositions. This term refers thentospeeds ofSO km/hr or more and includes thev speed of vehicles supported onair cushions, i.e., speeds-of 100 kmlhr to 300 km/hr.

To prevent wear of flexible bodi'esrubbing athigh speed on a rigidsurface a numberoflubricantscan be used. Lubricants are. known for low speed'operations',

such as greases, or oils, but thephysical-phenomenain- Y volved in low speed operations, in particular the relatively small amounts of heat which areliberated, arev very different from the physical jphenomena which: occur at high speed wherea very substantial-amount of heat is liberated by friction. Accordingly, due to the melting of a solid lubricant or to.theviscosityreduction of a liquid lubricant, the lubricatingqualities required are very substantially different inhigh speed processes as compared with=low speedprocesses.

One can choose, a priori from amongall available lubricants, which are grouped, for discussion, into two classes: liquids and solids. Amongliquid lubricants,.areheavy viscous oils. It is known that rubbing generates Although various types of solid coatings: have been tested for preventing wear of flexible bodies such asrubber, most have proven unsatisfactory; For discussion, solid lubricants canpbe subdivided into two subgroups. Lubricants in the first of said subgroups reduce the wear of flexible bodies to a very slight degree, but

on the other hand have a long life, the lubricating coating. itself not being changed by the rubbing. This is the case, for example, with epoxy resins, polyester, and

Formica, a plastic based on melamine and phenol. Lubricants in the second of the said subgroups completely eliminate the wear of the flexible body. But, on the other hand, they wear down too fast to be used in dustrially. This is-the case, for example, with grafted polyethylene, deasphalting pitch, and of soft tars in general.

The primary object of the present invention is therefore to provide a method of avoiding the wear of flexible bodies rubbing at high speed on rigid bodies.

Another object of this invention is to provide a coating for rigid bodies whereby it is possible to avoid the wear of flexible bodies which rub at'their place of contact.

Still another object of this invention is to provide an anti-wear coating which is stable with time and under the atmospheric and other conditions acting onit.

It has been found, that paraffin compositions, whether or northey contain additives, are excellent antiwear coatings and provide very satisfactory results bothwith respect to wear of flexible bodies and with respectto the resistance of the composition itself. The paraffin composition of this invention can be applied to the surface of any rigid material, for example, concrete, bituminous aggregate, metal, wood etc.

The rigid material must have certain qualities to ensure satisfactory adhesion of the lubricating coating when the coating and the rigid material have no particular affinity or marked adhesive properties for one another. Concrete, for example, is porous and has a rough surface and'the compositions of the invention will fill the surface'pores making a smooth surface. The same considerations apply to rough, cast metallic surfaces which, however, are not porous. Neither porosity nor roughness are essential, however, where the rigid material or the lubricating coatinghave adhesive attraction for one another.

The-paraffin compositions of this invention are paraffins and waxes which are normally produced from petroleum. Paraffms from the dewaxing of petroleum distillates, especially those intended for the production of lubricating oils, as well as waxes of higher molecular weight, can be used. Waxes produced, for instance, from de-asphalted vacuum-distillation residues are satisfactory.

Althoughthe paraffins and the waxes by themselves are excellent coatings for rigid surfaces, other properties are required of these coatings, in order to prevent deterioration with time. ,It has been found that certain additives are capable of imparting to the initial paraffin wax, properties of adherence and of resistance to ther mal shock, thus guaranteeing long life of the coating.

Such additives may be polyolefins, for instance polyethylenes, polypropylenes, polybutenes or polyisobutenes. Among .the olefin polymerswhich are used are polystyrene, copolymers of ethylene and vinyl cyclohexane, copolymers comprising two or more of the above-mentioned monoolefins and butyl rubber, which is a copolymer of isobutene and isoprene containing a small amount(less than 5 percent) of isoprene. Among the polyolefins are those on which another monomer such as acrylic acid has been grafted in order to impart properties of adhesiveness.

Other additives which are used to dope the parafflns are copolymers of ethylene and a vinyl ester, such as vinyl acetate, ethyl acrylate and isobutyl ac-rylate. These copolymers, when incorporated into the paraffin These different additives can be incorporated in the paraffin either alone or in combination so as to impart to the coating of the rigid bodies an optimum antiwear effect with respect to flexible bodies and maximum resistance with respect to mechanical and climatic stresses. The quantities of additives which can be added to the paraffin vary greatly and are not of a critical nature. It is however essential that the paraffin itself represents a substantial part of the coating composition. For example, from I to 20 percent of a polymer or copolymer of monoolefin, butyl rubber or grafted polyolefin, from I to 20 percent bitumen or from 1 to 60 percent of a copolymer of ethylene and vinyl acetate, may be added. In the latter case, the copolymer of ethylene and vinyl acetate has an ethylene/vinyl acetate molar ratio which may vary within wide limits, for example, between 4 and 16.

The paraffin composition in accordance with this invention may also contain products known as coefficient-of-friction depressors. These are, for example, graphite, molybdenum disulfide and certain phosphates.

It has been found that even a very slight thickness of paraffin composition retains its anti-wear properties. The quantity of paraffin composition which is used to cover a unit of surface depends on the roughness and the porosity of the surface to be coated. Below about 0.5 kg/m on concrete, for example, the coating becomes insufficient and wear will take place. The amount of paraffin composition should, therefore, be at least 0.5 kg/m'.

The application of the composition to the rigid surface can be effected by means known from paraffin application technology. Two techniques are best suited:

1. application by roller; and

2. spraying.

The spray method is best carried out by preheating the compressed air which feeds the spray gun and also preheating the surface of the concrete. In this way, excessively rapid solidification of the paraffin is avoided and the latter penetrates into the pores of the concrete. Good mechanical adherence is assured and a perfectly smooth protective film is obtained. The heating of the surface of the concrete can be effected by means of a flame or air torch or by radiation heating.

One particularly interesting application of this invention is in the field of vehicles which travel on air cushions, in particular air cushion (hover) vehicles guided by one or more rails. The aprons, which confine the air cushion which supports and guides the vehicle, are subjected to rapid wear due to accidental and more or less haphazard contact with the rail. The rail is generally made of concrete. Much wear on the rail occurs at the time of braking the vehicle. The compositions of this invention make it possible to substantially reduce the wear of the rubber aprons used on air cushion (hover) vehicles.

The invention is further illustrated by the following drawings and examples.

In the drawings:

FIG. 1 shows the variation of the coefficient of friction of various lubricating mixtures consisting of paraffin 58/60 and a copolymer of ethylene and vinyl acetate;

FIG. 2 sows the variation of the coefficient of friction of mixtures based on wax 20/30 and polyethylene;

FIGS. 3 and 4 show the wear of a rubbing member in millimeters and grams, respectively, as a function of the number of its contacts with and its speed with respect to a tract coated with epoxy-polyamine resin;

FIG. 5 shows the wear of a rubbing member comprised of VOLKOLLAN, expressed in grams, after 6,000 contacts at 145 km/hr with a track coated with mixtures containing paraffin 5 8/60 and a copolymer of ethylene and vinyl acetate, as a function of the percentage of copolymer in the lubricating mixture; and

FIG. 6 shows the wear of a lubricating coating based on wax 20/30 and polyethylene, after 6,000 contacts at 145 km/hr as a function of the percentage of polyethylene in the lubricating mixture.

The curves in the drawings graphically present the overall results obtained in the following Examples, which illustrate the invention.

EXAMPLE I The purpose of this example is to demonstrate the physical properties of the compositions of the invention. Several mixtures were prepared based on paraffin wax, with the addition of variable amounts of copolymer of ethylene and vinyl acetate or of polyethylene.

The coefficient of friction was measured for various mixtures as a function of rubbing speed. Curves 1, 2, 3, 4, and 5 in FIG. 1 and curves 6, 7, and 8 in FIG. 2 show these coefficients. The various compositions used in these tests are set forth in Table 1.

In Table 2 are given the mixture conditions and the principal characteristics of the products obtained, namely, penetration at 25 C, ball-ring (ASTM) temperature and dropping point.

TABLE 1 wt wt wt wt Paraffin Elvax" wax Polyethy- Fig. Curve 58/60 20/30 lene I00 0 l l 90 10 l 2 20 l 3 60 40 I 4 40 60 l 5 I00 0 2 6 10 2 7 Copolymer of ethylene and vinyl acetate.

Mixture conditions Characteristics Penetration Ball and Dre Product 7 M xture time Temperatures at 25C ring Paraffin /10 Paraffin+ 10 percent Elvax* 12/10 Paraffin percent Elvax.. 9/10 Parafiin percent Elvax.. 7/10 Paraffin percent Elvax 3/10 to 6 hrs. Wax 10/30 27 Wax+ 10 percent P.E.. 4 Hrs 120C 17/10 91.6 Wax+20 percent P.E.. 6 Hrs... 120C 14/10 94.4 Wux +40 percent P.E 6 Hrs 120C 8/10 99.4

All these mixtures were made under nitrogen blanket. Elvax is a copolymer of ethylene and vinyl acetate.

EXAMPLE ll RIKEN BAYER AG comprising polyurethane. The dimensions of the rubber for these tests are 10 mm X 5 In order to test the coatings of this invention, amamm X 5 mm. The rubbing body rubs on the track along chine is formedcomprising a rubbing body of flexible 20 its smallest cross-section and the presence of the rubrubber material anda track formedof ordinary cement bing member on the track is about 2 kg/cm Each of of 0/3 sand, poured into a circular aluminum mold. the coatings is applied by a spray gun and the thickness After the setting of the concrete, the entire unit is of the layer is such that the average application of coatsanded,'balanced and coated with the coating and then ing is 0.5 kglm mounted on the mandrelof the machine. A kinematic 25 The concrete coated with each of the coatings is then chain provides a linear rubbing speed of about 100 placed on the mandrel of the machine described above km/hr. The rubber is mounted on amovable armv held and the latter is' placed in operation. After a number of by an electromagnet. This electromagnet releases the cycles, depending on the apparatus wear, measuremovable arm, which results in periodic rubbing of the ments are made as described above. The results obrubber on the track, for a short time. The wear of the 30 tained'with different coatings are set forth in Table 3 rubber and the hollowing of the coating are measured, below. In Table 4 the results obtained with paraffin wax as a function of the number of cycles, i.e., the number and petroleum wax compositions are set forth for comof rubbing contacts. parison. The polyethylene which dopes the paraffin In all the following tests the rubbing body consists of wax is polyethylene of a molecular weight of about VULKOLLAN rubber, a product of the FARBENFAB 3 5 20,000.

TABLE 3.-COMPARISON 0F LUBRICATING PRODUCTS (SOLID LUBRICANTS) (Tested at about 100 kilometers/hour) Time of contact between f Lubricating product rubbing member and track Wear of the track Wear of the rubbing Conclusion of the test i Polyester A second every 10 seconds No wear-deposit of the Extremely severe wear after Abrasion and fusion of the material of the W 1000 cycles. H rubbing member.

| rubbing member.

Z Grafted Polyethylene 5 seconds per 60 seconds. Cement bared in L6 hour 0.3 mm in 5 sec. contact Premature wear of the coating.

I Grafted Polyethylene-78%/ 5 seconds per 60 seconds. Slight wear 0.2 mm in 5 sec. contact This is the best result obtained I Grutite-20%/Cabot Y with a coating containing a Monarch Black-74.2%. major portion of grafted polyethylene without paraffin wax product.

, Epoxy resin... 5 seconds per 60 seconds. No wear-deposit of material 2 mm in 5 sec. contact Track too abrasive. Heat deof the rubbing member.- velopment too excessive.

Formica (Melamine and phenolic 1/ 10 second per 1 second No wear-deposit of material 2.3 mm in 10 sec. contact Track too abrasive. Heat deplastics). of the rubbing member. velopment too excessive. Industrial bitumen (Type l/l0 second per 1 second Good appearance of the track... 1.0 mm in 1,000 cycles Result good but the rubbing "90-40"). member still wears out i slightly too much.

TABLE 4.-BEHAVIOR OF THE PARAFFIN WAX COMPOSITIONS UNDER REPEATED STRESSES -(Tested at about 100 kilometers/hour) Wear of the v Time of contact between Number o f Wear of the rubbing Conclusion of tli's riset nslf s ys w rubbing L and track contacts track "ren er the te I Pure paramnwax (Type 58/608) 14: second every 10 seconds 5,000 Good appearance Less than Excellent Y Y of the track. 0.1 mm. result. Pure paraffin wax 58/60 doped with 2.5% wt polyethylene ..do 5,000 ..do No apparent Do. I Pure paraffin wax 58/60 doped with 10% wt polyethylene. do 5,000 Do. Pure paraffin wax 58/60 doped with 15% wt polyethylene. do 5,000 Do. I Pure paraffin wax 58/60 doped with 20% wt polyethylene. ..do.. 5 ,000 Do. a 10% wt pure paraffin wax 58/603 30% wt Elvax" l/l0 secon every secon 5.... 5,000 Do.

1 i 80% wt pure purumn wax 58/608 15% wt Elvux' 5% wt butyl t a second every 10 seconds 10,000 Good appearance of Negligible Do. i rubber. the track. wear of the rubbing member 65%bvb1t p e P fi wax 58/608 30% wt E v x 5% t b tyl ..do 10,000 ..do ..do Do.

ru er. wax 20/30 refined 10% polyethylene ll 10 second every 6 seconds 4,000 Slight rutting of About 0.1 Good the track. mm. result.

*Elvax is a copolymer of ethylene and vinyl acetate.

The foregoing data prove that the best results are obtained with paraffin wax and petroleum wax compositions.

EXAMPLE Ill track; and

2. wear of the coating on the track, or its appearance after a certain number of contacts.

As can be seen in the following results, the two wear measurements depend on the materials, the speed and the number of contacts. The other parameters are not changed, i.e., the pressure of the rubbing member on the track and the ambient temperature of the test. The results therefore can be compared.

Where the Bitumen 90/40 coating is used, there is significant wear of either the track or of the rubbing member, depending on the speed. At low speeds, under about 50 km/hr, the track is bared after 1,000 contacts. At higher speeds, there is a significant deposit of The results are summarized in Table 5. The Example VULKOLLAN rubber on the track, so that after some shows that the life a pure paraffin lubricating coating contacts the rubbing member rubs on VULKOLLAN is shortened when subjected to the influences derubber and wears very quickly. For example, at a speed scribed. The inclusion of an additive such as polyethylof about 150 km/hr and after 300 contacts, the rubbing ene or a copolymer greatly reduces the deleterious efmember has lost nearly one half of its weight. fect of such influences. Where the epoxy-polyamine resin coating is used,

TABLE 5 Rubbing Contact time rubber member Lubn'calins Product Pre-treatment member track Track wear wear Conclusion Pure paraffin wax 581608 thermal shocks lw second every 6 seconds or Q3gs di s tn uliu itigs.... ..V....V.... Coati g n0! fl e I; second every 10 seconds. with time. Pure paraffin w a x 58/60B+2.5% ..do ..do Same as above to a lesser Good result but polyethylene. extent. decrease of the life of the track.

Pure paraflin wa x 58/608 l0% ..do /4 second every 10 seconds Good appearance polyethylene.

Do ..,..'d0 .4... lro second every 6 seconds Good appearance after 10,000 0.1 mm Excellent result.

contacts. Paralfin wax 58/608 [0% 72 hours under 600 /ro second every 6 seconds Good appearance of track, 0.2 mm after Good result.

r1v 5 Lo syssmz aurean, 99! o actsseveral tests at different speeds were carried out. At

EXAMPLE IV This Example demonstrates the use of one of the lclairned paraffin compositions for the lubrication of a flexible body rubbing at different speeds on a rigid su r nice; The rubbing speed varies from about lOltilometers per hour to about 300 km/hr. The contact pressure of the rubbing member on the track is 2 kg/cm. In all the tests-the rubbing body consists of VULKOLLAN rubber, a product of the FARBENFABRIKEN BAYER AG comprising polyurethane. The dimensions of the rubber are l0 mm X 5 mm X 5 mm and it rubs on the track along its smallest cross-section. The time of contact between the rubbing member and the track is a quarter of a second every ten seconds. For these tests the track is successively coated with three lubricants:

a. with an epoxy-polyamine resin, well known for its adherence to concrete, its water resistance and its long life as a coating;

b. with a Bitumen 90/40 which has many economic advantages; and c. with a paraffin wax and polyethylene composition typical of the invention.

After the test two measurements were made:

1. wear of the rubbing member which corresponds to the wear of any flexible body rubbing on the coated low speeds, from 20 to 30km/hr the track is slightly hollowed after 1,000 contacts, and the rubbing member is worn very slightly. At higher speeds, the rubbing member is worn very quickly and its loss of weight increased with increasing speed or number of contacts. For example, at a speed of about km/hr and after only contacts, the weight loss is about 60 percent. WEEERTQEFe xperTmt-Etistlien continued, this loss of weight increases very quickly with the number of contacts. Thus, although the weight loss of the rubbing member at high speeds is rather small, this coating is not satisfactory because wear increases too quickly with rubbing speed and with the number of contacts.

For comparison, a third coating typical of the invention is tested. The composition consists of:

Paraffin wax 58/60 75% wgt Elvax 260 17% wgt Escorez 6% wgt Alcatene 2% wgt (Elvax 260 is a polyethylene-vinyl acetate copolymer, about 28 percent wgt vinyl acetate; Alcatene is a commercial polyethylene; and Escorez is a petroleum wax.) In this test, the rubbing member does not wear at speeds varying from about 10 km/hr to about 250 .9. km/hr. The hollowing of the track is always slight. At low speeds there is abrasive wear due to the contact with the rubbing member. The coating composition is slightly stripped off. But at all speeds between km/hr' and 250 km/hr the depth of the rut is always under 0.2 mm after 6,000 contacts. The number of contacts is much greater than the number of contacts in the other tests.

These tests show that a coating composition according to the invention is superior to other coatings for decreasing the wear of flexible bodies rubbing at high speeds on rigid surfaces, because there is no wear of the rubbing member at different speeds where the track is coated with these compositions.

EXAMPLE V (Comparative Example) Tests are conducted as in Example IV with a lubricating coating of epoxy polyamine resin, and the wear of the rubbing member and of the track are measured as a function of the number of contacts and of the relative speed of the rubbing member with respect to the track. In FIG. 3 is shown the wear of the flexible rubbing member, the dimensions of which are here 75X5 5 mm. at different speeds (curves 9, 10, 11 and 12), in millimeters, and in FIG. 4 the same wear, measured in loss of weight of the flexible rubbing member (curves 13, 14, 15 and 16).

It can be seen that with a very small numberof contacts (less than 30.0), the rubbing member is almost completely worn if the speed exceeds 150 km/hr. The wear of the rubbing member increases very rapidly with speed. It is not possible therefore to use such a coating to lubricate movementat high speed. The wear of the rubbing member is, however, acceptable for low speeds (at 16.5 km/hr, for example).

EXAMPLE VI In this Example, it is desired to test various mixtures according to the invention at a speed of about 145 km/hr. Six thousand contacts are made between a flexible rubbing member of VULKOLLAN and a track coated l. with mixtures based on wax, to which are added various percentages of polyethylene; and

2. with mixtures based on paraffin, to which are added various percentages of Elvax. In both cases, the wear of the rubbing member was measured. For mixtures consisting of 100 percent wax 20/30, 90 percent wax 20/30 and 10 percent polyethylene, percent was 20/30 and 20 percent polyethylene, there is almost no wear in the rubbing member. With six mixtures consisting of paraffin 58/60 and Elvax, the measurements resulted in the data presented in curve 17 of FIG. 5. It can be seen, that beyond a substantial amount of Elvax (50 to 60 percent), the wear of the rubbing member increases very rapidly. The wear of the track coated with mixtures of wax and polyethylene is also plotted (curve 18, FIG. 6).

This Example proves that at high speed and for repeated contacts (6,000 contacts), mixutes according to the invention are very good lubricants for reducing the wear of a flexible body rubbing on a rigid surface.

What is claimed is:

l. A process for reducing the wear caused by friction of a flexible rubber body rubbing at high speed on a rigid surface of concrete, the said process comprising coating the rigid surface with at least 0.5 kg/m of rigid surface of a composition consisting essentially of 80 to 99 percent of a paraffin wax in a pure state and 20 percent to 1 percent of polyethylene.

2. A process as recited in claim 1 wherein the rigid surface is the guide and support rail of a vehicle which is supported on an air cushion. 

2. A process as recited in claim 1 wherein the rigid surface is the guide and support rail of a vehicle which is supported on an air cushion. 